Make `uv pip compile` attempt to download a specified `--python-version` if it can. by EliteTK · Pull Request #17249 · astral-sh/uv

EliteTK · 2025-12-29T12:59:39Z

Summary

Addresses #16709. Now specifying a simple version with --python or specifying a version using --python-version will result in the specified version getting downloaded with a fallback to the previous behaviour if the download fails for some transient reason or if downloads are disabled.

The behaviour of how --python gets treated as --python-version, if a "simple version" is specified, is kept. This means that --python 3.7 turns into a soft requirement. This seems at odds with how other similar parts of UV work, but there seem to be quite a few tests which test for this specific behaviour and I think this is best saved for a separate issue.

Test Plan

I added a test case which would previously fall back to the default interpreter and warn about it.

crates/uv-python/src/discovery.rs

…number.

crates/uv-python/src/discovery.rs

EliteTK · 2026-01-14T16:47:16Z

Heh... I just realised, what about if there's no default python version? We should probably also attempt to download in that final case too...

Most likely the reason will cause this one to fail too and handling the alternative case could add a delay (e.g. if it's a network failure which ends with retries and a timeout).

zanieb · 2026-01-14T17:47:29Z

Yeah that makes sense

EliteTK · 2026-01-14T21:09:03Z

Okay, I've refactored it all a little bit. Maybe the refactoring should have come first... Not sure.

Let me know what you think.

EliteTK · 2026-01-15T10:44:57Z

Should probably do something similar to #17461 too...

zanieb · 2026-01-15T13:36:22Z

I wouldn't increase the scope here :)

crates/uv-python/src/discovery.rs

zanieb · 2026-01-15T13:49:46Z

crates/uv/tests/it/pip_compile.rs

+    ----- stdout -----
+
+    ----- stderr -----
+    warning: A managed Python download is available for Python 3.10, but an error occurred when attempting to download it: Failed to download https://github.com/astral-sh/python-build-standalone/releases/download/[FILE-PATH]


The attached error is worthless. I think we need to render the chain?

Yeah I was curious about your opinion on this. I'll render the chain. Do you know off the top of your head if we do that somewhere else already? (I know how to do it, the anyhow docs have a good example (even if this isn't an anyhow error))

uv-warnings::write_error_chain

I'm not too sure about this formatting...

Shouldn't you be creating a fake top-level error so it's all one chain?

Didn't think of that... But the bold would be gone, it would look different to the warning below.

Still... Probably a neater look overall. Will sort it tomorrow.

I think that sounds like a bug in the warning chain print? Should it be bolding the first error in warnings for parity?

Co-authored-by: Zanie Blue <[email protected]>

This MR contains the following updates: | Package | Update | Change | |---|---|---| | [astral-sh/uv](https://github.com/astral-sh/uv) | patch | `0.9.26` → `0.9.27` | MR created with the help of [el-capitano/tools/renovate-bot](https://gitlab.com/el-capitano/tools/renovate-bot). **Proposed changes to behavior should be submitted there as MRs.** --- ### Release Notes <details> <summary>astral-sh/uv (astral-sh/uv)</summary> ### [`v0.9.27`](https://github.com/astral-sh/uv/blob/HEAD/CHANGELOG.md#0927) [Compare Source](astral-sh/uv@0.9.26...0.9.27) Released on 2026-01-26. ##### Python - Upgrade Pyodide to 0.29.2 ([#17652](astral-sh/uv#17652)) - Upgrade to GraalPy 25.0.2 ([#17634](astral-sh/uv#17634)) ##### Enhancements - Add `-t` shortform for `--target` to `uv pip` subcommands ([#17501](astral-sh/uv#17501)) - Add support for ROCm 7.0 and 7.1 accelerator backends ([#17681](astral-sh/uv#17681)) - Further improve free-threading ABI incompatibility errors ([#17491](astral-sh/uv#17491)) - Implement `uv pip freeze --exclude` flag ([#17045](astral-sh/uv#17045)) - Improve warnings for `--system` and `--no-system` in `uv venv` ([#17647](astral-sh/uv#17647)) - Make `uv pip compile` attempt to download a specified `--python-version` if it can. ([#17249](astral-sh/uv#17249)) - Support Trusted Publishing with pyx ([#17438](astral-sh/uv#17438)) - Fix JSON schema for `exclude-newer-package` ([#17665](astral-sh/uv#17665)) ##### Preview features - Better detection for conflicting packages ([#17623](astral-sh/uv#17623)) - Upgrade based on outdated build versions in `uv python upgrade` ([#17653](astral-sh/uv#17653)) ##### Bug fixes - Change chocolatey system test to ensure uv uses the right python ([#17533](astral-sh/uv#17533)) - Fix infinite loop when `SSL_CERT_FILE` is a directory ([#17503](astral-sh/uv#17503)) ##### Documentation - Add cargo-xwin to the CONTRIBUTING guide ([#17507](astral-sh/uv#17507)) - Fix typo in the documentation of UV\_PUBLISH\_INDEX ([#17672](astral-sh/uv#17672)) - Move MSRV to platform support section ([#17534](astral-sh/uv#17534)) - Update the testing instructions in the CONTRIBUTING guide ([#17528](astral-sh/uv#17528)) - Use `--locked` to install `cargo-xwin` in guide ([#17530](astral-sh/uv#17530)) - Warn about PyPy being unmaintained ([#17643](astral-sh/uv#17643)) - docs: Correct gitlab-ci.yml to .gitlab-ci.yml ([#17682](astral-sh/uv#17682)) ##### Other changes - Update MSRV to 1.91 ([#17677](astral-sh/uv#17677)) </details> --- ### Configuration 📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever MR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this MR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this MR, check this box --- This MR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).

Make uv pip compile attempt to download --python-version

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EliteTK added the enhancement New feature or improvement to existing functionality label Dec 29, 2025

EliteTK temporarily deployed to uv-test-registries December 29, 2025 13:01 — with GitHub Actions Inactive

EliteTK commented Dec 29, 2025

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EliteTK commented Dec 29, 2025

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EliteTK requested a review from zanieb December 29, 2025 13:05

EliteTK added 3 commits January 14, 2026 14:32

Move download handling to a separate function

82fc23b

Re-attempt a download when falling back to a version without a patch …

efe864e

…number.

Avoid errors which would previously have not occurred

2ac4a7f

zanieb reviewed Jan 14, 2026

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EliteTK added 2 commits January 14, 2026 16:49

Add a comment elaborating need to warn on download error

c2c8dc4

Don't attempt a second download if the first one failed for any reason

db0e72b

Most likely the reason will cause this one to fail too and handling the alternative case could add a delay (e.g. if it's a network failure which ends with retries and a timeout).

EliteTK added 2 commits January 14, 2026 18:51

Download python in the default fallback case too

5c3dcb7

Remove stuttery Result type

9cfa37e

EliteTK temporarily deployed to uv-test-publish January 14, 2026 19:53 — with GitHub Actions Inactive

EliteTK added 5 commits January 14, 2026 20:10

Roll everything into a loop

2aaec3d

Fix comments

e548074

Inline attempt_download again

63f4ef7

Restore some more comments

158444b

Fix error reporting bug?

2b70679

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EliteTK requested a review from zanieb January 14, 2026 21:09

zanieb reviewed Jan 15, 2026

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zanieb approved these changes Jan 15, 2026

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EliteTK and others added 3 commits January 15, 2026 16:57

Improved error handling comment

876704f

Co-authored-by: Zanie Blue <[email protected]>

Elaborate debug messages

260bc11

Rename installation -> result

e21a148

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EliteTK force-pushed the tk/pip-compile-missing-py-4 branch from b0133d4 to 9e29d97 Compare January 15, 2026 18:31

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EliteTK added 2 commits January 16, 2026 13:50

Write out the full error chain

f1c06dd

Print first error chain message in bold to match warn_user

8ac4906

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EliteTK merged commit f7d1215 into main Jan 16, 2026
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BrewTestBot mentioned this pull request Jan 26, 2026

uv 0.9.27 Homebrew/homebrew-core#264626

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EliteTK commented Jan 14, 2026

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EliteTK commented Dec 29, 2025 •

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